Add pskiplists subdir

CMakeLists.txt

@@ -102,6 +102,7 @@ add_subdirectory(src/pbptrees) # Persistent versions of B⁺-Tree, contains also
                                # - Remake of the wB+Tree
 add_subdirectory(src/ptable)  # BDCC-based analytical table structure
 
+add_subdirectory(/src/pskiplists) 
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 # Unit test using Catch #
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